The present invention relates to a thermal transfer image forming method used in a word processor, a facsimile or the like, and a combination of thermal transfer members which is used therein. More particularly, the present invention relates to a thermal transfer image forming method for forming an image having high fastness on various media by thermal transfer, the media including high quality paper sheets (paper sheets having a high surface smoothness), plastic films such as polyethylene terephthalate film, polypropylene film and vinyl chloride based resin films, and photographs; and a combination of thermal transfer members which is used therein.
For the purpose of forming images having high fastness on various receptors, a method has hitherto been adopted wherein fixing ability of an image to a receptor is improved by using an ink ribbon having, on its substrate, a color ink layer and an adhesive layer from the substrate side and making the adhesive layer of the ink ribbon of the same type of material as the material constituting the receptor. In order to realize an image having high fastness in this case, it is necessary to use, for the adhesive layer, a material having strong adhesion to the receptor. As the material having strong adhesion to the receptor, a resin having a high molecular weight or a like material needs to be selected and used. For this purpose, it is necessary to set a printing energy upon thermal transfer to a high value. This results in a problem that upon the thermal transfer the flatness of the color ink layer is damaged, causing a decrease in the density and chroma or saturation of the image. Particularly in the case of an ink ribbon, for forming a gloss image, having a metal deposition layer as its color layer, damage of the flatness of the color layer results in a problem that glossy impression is lost. Thus, in order to obtain an image having high quality and high fastness, it is necessary that ink ribbons in the prior art cope with each of diversified receptors.
Particularly in order to form a color image, it is in general necessary to prepare 3 kinds of ink ribbons (yellow, magenta and cyan ink ribbons) or 4 kinds of ink ribbons (yellow, magenta, cyan and black ink ribbons) having the above-mentioned structure. However, in order to obtain a color image having high fastness, adhesive layers of these ink ribbons need to be changed whenever the kinds of receptors change. For example, in the case that the above-mentioned 4 kinds of ink ribbons are used and 3 kinds of receptors, e.g., polyethylene terephthalate film (PET film), polypropylene film (PP film), and high quality paper sheets, are used, it is necessary that the number of kinds (N1) of the adhesive layers is 3. Therefore, in the case that the number of kinds (N2) of the ink ribbons (that is, color ink layers) is 4, 3 kinds of adhesive layers become necessary for each of the 4 kinds of color ink layers. After all, the number of kinds of necessary ink ribbons is 12=N1.times.N2. As described above, in order to form images having high fastness on various receptors according to the prior art, many kinds of ink ribbons are unavoidably prepared, resulting in a rise in costs.
In the light of the above-mentioned problems in the prior art, an object of the present invention is to provide a thermal transfer image forming method which makes it possible to easily cope with even an increased kinds of receptors due to diversification of receptors and to make the number of kinds of ink ribbons as small as possible, and to form images which are excellent in fastness; and a combination of thermal transfer members which is used therein.
Another object of the present invention is to provide a thermal transfer image forming method which makes it possible to reduce, as much as possible, restrictions originating from a demand of ensuring the fixing ability of an image to a receptor upon designing an ink layer of an ink ribbon; and a combination of thermal transfer members which is used therein.
These and other objects of the present invention will become apparent from the description hereinafter.